1. Technical Field
Example embodiments relate to semiconductor devices having a dielectric layer of a high dielectric constant and to a method of manufacturing semiconductor devices.
2. Description of the Related Art
As a result of semiconductor devices becoming more highly integrated, the area of a unit cell has been significantly reduced, and also the operational voltage has been lowered as well. Accordingly, a dielectric layer having a high dielectric constant (high-k) has been applied to the semiconductor devices to enhance electrical storage performance and/or to suppress leakage current through the dielectric layer.
Generally, a high-k dielectric layer has a thin equivalent oxide thickness and a high dielectric constant, so the high-k dielectric layer may improve the capacitance of a capacitor or a coupling ratio of a flash memory device, or the high-k dielectric layer may provide a proper threshold voltage of a metal gate structure.
For example, a hafnium oxide (HfO2) layer, a tantalum oxide (Ta2O5) layer or an aluminum oxide (Al2O3) layer have been used as the high-k dielectric layer. These dielectric layers have a high dielectric constant of about 20, so these dielectric layers may have an electrically effective thickness. However, these dielectric layers may be crystallized during a subsequent annealing process. When crystallization of a dielectric layer occurs, a threshold voltage of a gate may not be uniform along a channel length, and a leakage current deteriorating reliability of a semiconductor device may be generated.
Zirconium oxide (ZrO2) has a high dielectric constant of at least about 40, so recently zirconium oxide has been widely used as a dielectric layer. However, a zirconium oxide layer may have some difficulties with regard to deteriorating characteristics of a semiconductor device. For instance, the zirconium oxide layer may be readily thickened while other processes are performed. In addition, the zirconium oxide layer may be readily crystallized during a subsequent thermal process, so leakage current of a semiconductor device may be generated through a crystallized portion of the zirconium oxide layer.
FIG. 1 is a graph illustrating a failed bit count (FBC) according to variation of applied voltage (Vp) in a memory device having a zirconium oxide (ZrO2) dielectric layer. Referring to FIG. 1, the number of failed bit per unit cell rapidly increased at about 0.6V, and increased at about 1V largely over about 10 bit, which may be a maximum allowable number of failed bits. These results may indicate that leakage current paths may be generated in the zirconium oxide layer while amorphous zirconium oxide of the dielectric layer may be partially or fully crystallized by heat. Therefore, when a zirconium oxide dielectric layer is used, an increase in temperature in a thermal process may be limited. Therefore, the formation of a dielectric layer having enhanced thermal stability and electrical characteristics, e.g. a uniform threshold voltage in a channel region and a constant operational voltage, is still required in the art.